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Re: Psittacosaur tail structures


Jaime,
I agree it is a dead horse. I never thought the "balancing" counterargument to my hypothesis was much of a problem even in the context of just theropods (even less so now that the phylogenetic context is expanding).
And I was using thermoregulation in the broader sense. In the strict sense it refers to internal regulation of the animal itself. But there is also external thermoregulation of the nest, eggs, and babies (once they've hatched). I agree with Hopp and Orsen that such external thermoregulation evolved first and that internal thermoregulation came later (and aerodynamic exaptations even later).
My theory is that even external thermoregulation (brooding) was exapted from an earlier purpose, that it probably occurred on the tail, and initially perhaps only on the end of the tail.
Could have been for display, but I think predator evasion is a better hypothesis. If these long hairlike protofeathers extended beyond the tip of the tail, some pursuing predators may have gotten just a mouthful of hairy keratin. If some predators got part of the tail as well, it's still obviously a lot better to lose part of your tail than to lose your life. Psittacosaurs may have been in the process of losing such structures if they were no longer needed for display or whatever (the predator evasion strategy would have no doubt been long since abandoned by their smaller ancestors). But it psittacosaurs had them on their bellies as well, that would probably indicate the brooding (external thermoregulatory) function was still used.
-------Ken Kinman
P.S. My apologies for misspelling Headden and Hopp in my post yesterday. But this news of tails with long "hairs" in psittacosaurs had me rather excited. Still does. Really COOL news even if it isn't "official" yet. Almost as cool as when fossil evidence was recently found that eurypterids and scorpions do form a clade (validating the recogition of Classes Scorpionea and Arachnidea).
******************************************* 
From: "Jaime A. Headden" <qilongia@yahoo.com>
To: dinosaur@usc.edu
CC: kinman@hotmail.com
Subject: Re: Psittacosaur tail structures
Date: Sun, 12 Aug 2001 00:00:51 -0700 (PDT)

Okay, I read the days mail before I set to writing this, to make sure
I wasn't repeating anything ... besides the dead horse that I will
bring up....

Ken Kinman (kinman@hotmail.com) wrote:

<(even wing feathers would have been initially thermoregulatory, as
favored by Tom Hopps and others).>

  Not entirely accurate. Hopp and Orsen's theory, not bandied about
as much as it should, suggests that they are not intended to regulate
the animal's own thermogenesis, but to regulate ambient temperature
of the nest, as an umbrella, and only secondarily acheive
aerodynamics. They are not thermoregulatory in the sense of body
"feathers".

<If this stage occurred in early dinosauromorphs, it would perhaps
make balancing problems (brought up by Jaime Headdin) from loss of
part of the tail even less of a problem for my hypothesis. Such a
predator evasion strategy would have worked especially well in forms
that had long slender tail tips (wiggly, but with little mass).>

  Err ... this kind of tail would have had no balancing capabilities,
having little mass or inertial/impetus/balance control, and the same
hold true for any extra-integumentary structures like protofeathers,
these in *Sinosauropteryx* being hollow filaments forming a small,
fan-like spread. The implication is that of aerodynamics, or display,
rather than any "lure" or weak point to be snapped at. Again, dead horse.

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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